1. Field of the Invention
This invention relates to a hybrid thermoelectrochemical process for production of gaseous fuels from water and carbon dioxide. The process provides a simple hybrid thermoelectrochemical reaction couple of the thermochemical reaction of reforming methane using carbon dioxide or steam and the electrochemical reaction is reduction of the reforming product producing a net gaseous fuel and oxygen for withdrawal from the cycle and methane for recycle. The reforming step can be driven by solar or nuclear thermal energy while the electrochemical energy can be supplied by a solar photovoltaic or nuclear driven generator.
2. Description of the Prior Art
Gaseous fuels which have methane as a principal component are presently derived from natural gas supplies which, as a natural resource, are finite. Methane-rich fuels can also be derived from coal or other natural carbonaceous sources which are also generally finite. It would be advantageous to provide new sources of methane-rich gaseous fuels based upon renewable or sustainable energy sources. It would be especially advantageous to use inorganic feeds such as water and carbon dioxide to produce methane-containing fuels.
Steam reforming of methane is a known reaction practiced in a number of processes as exemplified by U.S. Pat. Nos. 1,734,559, 2,256,333, 2,665,199, 2,743,171, 2,942,958, 3,090,682, 3,132,010, 2,199,475, 2,266,989, 2,526,521, 2,529,630, 2,607,670, 2,859,103 and 4,182,746. Carbon dioxide reforming of methane is not a commerical process, but is being investigated in several laboratories. Fraenkel, D., Levitan, R. and Levy, M., "A solar Thermochemical Pipe Based on the CO.sub.2 --CH.sub.4 (1:1) System", Int. J. Hydrogen Energy, 11, 267, 1986 teaches a solar powered thermochemical pipe based upon closed loop dry methane/carbon dioxide catalytic reforming reactions for heat storage and extraction. The process proposed by Fraenkel et al does not result in a net fuel output.
U.S. Pat. Nos. 3,766,027 and 3,852,180 teach methane production from water and carbon dioxide by use of electrical energy to drive water electrolysis producing a mixed gas product from which methane may be separated.
Use of coal, oil shale and tar sands gasification products including hydrogen/carbon monoxide mixtures in the electrochemical production of methane under high temperature laboratory conditions is taught by the Gur et al references, Gur, T. M. and Huggins, R. A., "Methane Synthesis on Nickel by a Solid-State Ionic Method", Science, 219, 967, Feb. 25, 1983; Huggins and Gur, U.S. Pat. No. 4,404,068; and Gur, T. M. and Huggins, R. A., "Electrolcatalysis of the Carbon Monoxide Methanation reaction on Stabilized Zirconia", Proc. of the Symp. on Electrocatalysis, Electrochem. Soc., Pennington, N.J., 1982.
A number of closed cycle reactant regenerative processes for splitting water are known, as taught by U.S. Pat. No. 4,332,650. A methane-methanol three step cycle for water splitting by: steam reforming methane; conversion of the products to methanol; and electrochemical reduction of methanol to methane and oxygen is taught by Biallas, B., Behr, F., Hunsanger, K., Kugler, B., Weirich, W., "The Methane-Methanol Hybrid Cycle", Hydrogen Energy Progress IV, Proceedings of the 4th World Hydrogen Energy Conference, California, USA, edited by T.N. Veziroglu, W. D. VanVorst, J. H. Kelly, 1982.
The prior art known to the applicants has not suggested a simple, two step, hybrid thermoelectrochemical cycle providing net production of gaseous fuel from water and carbon dioxide.